1. Field of Invention
This invention is directed towards raster output scanners that include double-pass sagittally offset pre-polygon optics.
2. Description of the Related Art
Electrophotography, a method of copying or printing documents, is performed by exposing a light image representation of a desired original image onto a substantially uniformly charged image carrying member. Imaging systems obtain read information based on original image data and image light beams onto the image carrying member representing the original image data.
An imaging system assembly may include a light source, pre-polygon optics, a scanning device including a polygon mirror, and post-polygon optics. The light source emits at least one light beam which passes first through the pre-polygon optics. The pre-polygon optics collimates the light beam in the fast scan direction and converges the light in the cross scan direction to a line focus on a polygon facet of the rotating polygon mirror. The rotating polygon mirror in the scanning device rotates around an axis of rotation, while the active facet of the polygon mirror reflects the light beam to the post-polygon optics. As the current facet scans the beam in the scan direction, an image carrying member is moving in a process direction which is perpendicular to the scan direction. Each light beam reflected from the current facet of the rotating polygon mirror passes through the post-polygon optics and is imaged onto the image carrying member to form an image.
In various embodiments of imaging systems, a double-pass optical system may be applied. In a double-pass optical system, the pre-polygon optics and the post-polygon optics are provided by a single set of optical elements. Accordingly, the light beam propagates through one or more double-pass optical elements of the pre-polygon optics, including pre-polygon scan lenses, before reaching a facet of the polygon mirror, and then propagates back through those one or more double-pass optical elements of the post-polygon optics before reaching the image carrying member.
This invention provides a double-pass optical system that reduces the number of double-pass optical elements.
In various exemplary embodiments of the double-pass optical system of this invention, the double-pass optical elements include a hybrid toroidal diffractive optical element.
In various other exemplary embodiments of the double-pass optical system of this invention, the double-pass optical elements include refractive cross-cylindrical optical elements.
In various other exemplary embodiments of the double-pass optical system of this invention, the double-pass optical elements include refractive spherical and cylindrical optical elements.
In various other exemplary embodiments of the double-pass optical system of this invention, the double-pass optical elements include a refractive sagittal cylindrical optical element.
In various other exemplary embodiments of the double-pass optical system of this invention, the double-pass optical elements include a refractive tangential cylindrical optical element.
In the double-pass optical system of this invention, advantages such as lower cost and ease of alignment are achieved.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the systems and methods according to this invention.